WASHINGTON (AFP) - A new poll Monday showed Hillary Clinton losing a general election to all potential Republican White House foes, in a new sign that fierce political attacks may be harming her 2008 campaign.

But the Democratic front-runner insisted she would win the party presidential nod, and warned she would take on her newly aggressive opponents head-on, just 38 days before Iowa's leadoff caucus nominating contests.

The Zogby International hypothetical 2008 matchup, reversing months of Clinton dominance over the Republican field, came as her camp battled in an ugly new spat with her top Democratic rival Barack Obama.

The Illinois senator meanwhile said chat show queen Oprah Winfrey would sprinkle showbiz stardust on his campaign in a three-state swing in December.

He also issued a sarcastic appraisal of Clinton's claims of top level political experience, during her eight years at husband Bill Clinton's side as first lady between 1993 and 2001.

"Senator Clinton is claiming basically the entire eight years of the Clinton presidency as her own, except for the stuff that didn't work out, in which case she says she has nothing to do with it," Obama said in an ABC News interview to be broadcast later Monday.

He compared conversations between the former president and his wife with his own talks with his own spouse.

"I don't think Michelle would claim that she is the best qualified person to be a United States senator by virtue of me talking to her on occasion about the work I've done."

The Clinton campaign hit back hard, driving home her argument that Obama would need "on the job training" in the White House.

"Considering that Senator Obama was a state senator just three years ago, he is the last person to be questioning anyone's experience," said Clinton spokesman Phil Singer.

"If he is elected, he would have less experience than any American president of the 20th century."

The Zogby poll reopened a simmering debate in the Democratic presidential field over which candidate has the best chance to beat a

Republican in the general election showdown in November 2008.

In hypothetical 2008 matchups, it showed Clinton trailed Senator John McCain 42 percent to 38 percent, ex-mayor of New York Rudolph Giuliani by 43 percent to 40 percent and former Massachusetts governor Mitt Romney 43 to 40 percent.

She also lagged behind former Arkansas Republican governor Mike Huckabee by 44 to 39 percent, and former Senator Fred Thompson by 44 to 40 percent.

Clinton's top Democratic challengers Obama and John Edwards however would still beat their hypothetical Republican rivals in potential 2008 contests, the poll showed.

In July, Clinton held a five point lead in the same poll over Giuliani, edged out McCain by two points and had a clear lead over other contenders.

A Rasmussen poll last week had Clinton also falling behind Giuliani in a November 2008 matchup and narrowly beaten by McCain.

An average of all previous similar polls however gives Clinton a narrow lead over possible Republican candidates, and the former first lady still leads most state and national polls.

An ABC News/Washington Post poll last week in Iowa however gave Obama the slimmest of leads over her and former vice presidential nominee John Edwards.

Clinton has repeatedly portrayed herself as the most electable Democrat after years standing up to what she calls the "Republican attack machine."

"I have absorbed a lot of attacks, my opponents have basically had a free reign," she told CBS News in an interview on Monday.

"After (being) attacked as often as I have from several of my opponents, you can't just absorb it, you have to respond."

Clinton also dismissed the idea that one of her rivals could deprive her of the Democratic nomination. "It will be me," she said.

The Zogby poll was conducted online among 9,150 likely voters across the United States between November 21 and 26, and carried a margin of error of plus or minus one percentage point.

The former first lady will hope to use the debate, 21 days before the Iowa caucuses, to halt her rival’s momentum, and repair her former aura of invincibility.

But Obama, a first-term senator hoping to become the first African-American president, will try to stay above the fray, supporters said, as he rams home his claim that Clinton is a symptom of poisoned US politics, not a cure.

Clinton enjoys a wide lead in national polls, but in the last few weeks has watched her advantage disappear in the crucial first two states to hold nominating contests, Iowa and New Hampshire.

Obama has now slipped ahead of Clinton by a couple of points in a Real Clear Politics.com average of Iowa polls, though the race remains a statistical dead heat.

A CNN/WMUR poll in New Hampshire meanwhile had Clinton just edging Obama by 31 percent to 30 percent.

She was down five points and Obama was up eight from the same poll in November. The New Hampshire primary is on January 8.

The New York Daily News reported on Wednesday that former president Bill Clinton, renowned as the most gifted politician of his generation, was increasingly dismayed over his wife’s prospects.

The paper said the ex-commander in chief was "furiously plotting a cure —or coup," in her campaign staff, in an 11th hour intervention to get her potentially historic bid to be America’s first woman president back on track.

The Clinton campaign did not respond to a request for comment, but sources close to the former first lady dismissed the notion in a story on the Politico.com, website.

The New York senator told senior staff on Tuesday that talk of a shake-up was "ludicrous" and said "why would anyone believe this nonsense?" a source told the Politico.

Analysts said Clinton faced a difficult task in trying to contrast her packed resume with what her campaign says is Obama’s dangerous lack of experience for a potential president.

Attacks by her aides on Obama earlier this month, including references to a kindergarten essay he reportedly wrote about how he wanted to be president — supposed evidence of overweaning ambition — appeared to backfire.

And with Iowa voters, who are renowned for making up their minds late about candidates, notoriously loathe to embrace negative attacks, a leading man on Clinton’s campaign in New Hampshire, hastily apologised just hours after bringing up Obama’s past drug use.

"I deeply regret the comments I made today and they were not authorised by the campaign in any way," Bill Shaheen said in a statement issued by Clinton’s campaign.

Shaheen had told the Washington Post that Republicans were certain to attack Obama for his past drug use, including marijuana and cocaine, which Obama has acknowledged as a folly of his youth in a published memoir.

"I will be, ‘When was the last time? Did you ever give drugs to anyone? Did you sell them to anyone?" Shaheen said.

"There are so many openings for Republican dirty tricks. It’s hard to overcome."

Obama’s campaign manager accused the Clinton campaign of making an "increasingly desperate effort to slow her slide in the polls," and "recycling old news that Barack Obama has been candid about in a book he wrote years ago."

Obama rides into the debate basking in favorable headlines after a weekend campaign swing with US talk show diva Oprah Winfrey.

But most analysts say that he has failed to hit the heights of his soaring rhetoric in set-piece speeches, in the flurry of Democratic debates so far, and sometimes comes across as plodding and professorial.

Clinton has an opportunity as well as a challenge heading into the debate, said Dennis Goldford, professor of political science at Drake University, Iowa.

"She wants to show Democrats she is tough enough to take on a Republican, but if she shies away from taking on Obama, she contradicts her own argument," Goldford said.

Third-ranked Democrat John Edwards, the former party vice presidential nominee, will be hoping that Clinton and Obama will cut one another to pieces, and allow him to surge through the middle. — AFP.